1. Field of the Invention
The present invention pertains to performance analysis of instrument controlled spraying. In particular, the present invention pertains to the use of image processing techniques to determine as-sprayed drop statistics for sprayed witness cards (WC's).
2. Description of the Related Art
A wide variety of manufacturing and agricultural processes rely upon the use of instrument controlled spraying. For example, farmers and foresters typically use aircraft and/or farm equipment equipped with instrument sprayers to apply fertilizers and pesticides. Manufacturers use spray techniques to apply coatings and/or layers of a prescribed density and/thickness.
In the case of farming and forestry, the spraying process preferably results in a prescribed amount of fertilizer or pesticide being distributed uniformly to the ground, crop or trees. A spray that distributes too little fluid to a target area may reduce the effectiveness of the fertilizer or pesticide treatment, resulting in lost crops/trees and/or reduced yield. A spray that distributes too much fluid to a target area typically increases the cost of applying the treatment and may result in additional losses due to undesired side effects and/or pollution. A spray that distributes fluid to a target area unevenly, typically results in some portions of the sprayed area receiving too little treatment and other portions of the area receiving too much treatment, resulting in both types of losses described above.
Manufacturing environments, such as automobile production plant paint shops, plywood manufacturers, coated glass manufacturing, and other processing facilities typically used sprays to apply paint, adhesives, cleaning solutions, etc., at various steps of the production line. The ability to deliver a precise distribution of a sprayed solution in a specified period of time allows such plants to conserve resources, reduce waste, and to optimize a production line for consistent production.
In recent years, the ability to quantify the effectiveness of military and homeland security detection equipment designed to detect pollutants, toxic chemicals and/or biological agents within an environment has further increased the need for a fast and effective determination of spray characteristics as applied to a target area. For example, a laser interrogation system scans an operational environment to detect trace amounts of substances using Raman Spectrum based analysis. In order to perform operational testing of such a system, the precise nature of a sprayed distribution within the operational test must be precisely known.
The performance instruments used to dispense a fluid in the form of a mist, or spray, is typically quantified in terms of volume per unit time. This, plus sprayer motion results in a desired spray density and a mass median diameter (MMD) of droplets deposited upon a sprayed target. Spray density quantifies the number of droplets deposited within a predetermined area. Mass median diameter is the diameter for which one-half of the mass sprayed upon a target is contributed by particles smaller than the MMD and one-half of the sprayed mass is contributed by particles larger than the MMD. For example, if 1001 mg of solution is sprayed upon a target, the mass median diameter is the particle size such that 505.5 mg are contributed by particles smaller than the MMD and 505.5 mg are contributed by particles larger than the MMD. Assuming that each droplet is substantially spherical, measures of spray density and MMD provide a measure of the coverage achieved with the spray.
Currently, there is no reliable mechanism for setting an instrument controlled spraying device to deliver a precise spray of a selected fluid to a target. If droplets within a spray are too small, the droplets tend to drift away from their intended target, resulting in a low spray density and poor coverage. Larger droplets resist drifting, however, if the droplets are too large, a low spray density, and hence poor coverage, is again achieved. Further, the same control setting upon a spray device may result in a different as-sprayed result upon a target area due to a variety of external factors such as the temperature of the fluid being sprayed, the viscosity of the fluid at the current temperature, the distance of a target from the spray jet, the presence/absence of wind, high/low humidity, high/low ambient temperatures, and/or other factors which can cause portions of a spray to drift off and/or portions of the spray to evaporate prior to reaching a target.
The inability to control such spray characteristics via a spraying device, especially with respect to agricultural, forestry and military test operations, in which fluids are typically sprayed from aircraft and/or ground vehicles operating in relatively uncontrolled environments, requires that a spray's characteristics be sampled/monitored within a sprayed area in order to determine the spray characteristics achieved by a specific sprayed application. Such sampling/monitoring is also helpful in controlled environments such as production lines to periodically ascertain the as-is characteristics of an applied spray.
Typically, such monitoring is performed by laying down paper or cardboard cards, commonly referred to as witness cards, at one or more locations within an area to which a spray is to be applied. The witness cards absorb the sprayed drops resulting in a fixed pattern of stains of varying sizes deposited on the cards. Thus, each card captures a representative sample of the spray at a location within the sprayed area. Once stained, a witness card is analyzed and the stain pattern is translated into a characterization of the spray in terms of spray density, MMD and other statistical parameters.
Unfortunately, conventional techniques for processing witness cards are quite limited. For example, one technique is to take pictures of small portions/samples of a witness card and to manually assess the droplet stains found within each successive sample. A single witness card is typically sampled until a maximum of 15 portions/samples are processed or until information on 100 droplets is collected. Information related to the droplet stains is used to characterize the spray at the location of the witness card. By collecting information related to multiple witness cards distributed over an area subjected to a spraying operation, statistics related to the overall spraying are generated.
The above process is typically performed manually, with visual aids. Assessment of fifteen witness card portions/samples or 100 spots per card have conventionally been considered sufficient to statistically characterize the spraying operation with respect to the witness card. However, despite the use of such statistical methods, the process typically takes several weeks to complete. During that time, an individual selects and processes portions/samples on each witness card and feeds the collected witness card stain analysis information into a computer that computes a spray density and MMD for the spray. Such an approach is susceptible to significant variation due to the possibility of human error with respect to the witness card portion/sample areas selected for assessment and human error with respect to determining the diameters of the identified stains.
Hence, a need remains for a method and apparatus that allows the performance of a spray device to be quickly and accurately assessed. Preferably, such an approach would provide a direct quantitative assessment of spray device performance based upon an assessment of a greater number of available spray droplets rather than relying upon sampling techniques, thus avoiding human judgment error associated with current sampling techniques. Further, the spray performance analysis would preferably be capable of being performed by technicians without specialized experience or special stain analysis knowledge and/or training.